Nanostructured Vitamin E Phosphate: Characterizing its percutaneous Penetration into Excised Human Skin and release from cosmetic formulations

Co-authors : M.M. SALEH 1, R. ABU HAMDAN 1, W. ALSHAER 2, M. AMARIN 3

1 Department of Pharmaceutics and Pharmaceutical technology, School of Pharmacy, The University of Jordan, Amman 11942, Jordan

2 Cell therapy Center, The University of Jordan, Amman 11942, Jordan

3 Jordan University Hospital, Amman, Jordan

Modern topical sunscreens combine topical antioxidants with physical UV filters to achieve optimal skin protection1–3. α-Tocopherol phosphate (α-TP), a new pro-vitamin E antioxidant, prevents UVA1 induced cell death and scavenges the reactive oxygen species that are produced in skin cells4. The aim of this study is to investigate if α-TP in candidate vehicles can penetrate excised human skin. This study also aims to prepare solid lipid nanoparticles (SLNs) that can act as a physical sunscreen, containing α-TP and evaluate for encapsulation efficiency (EE) and skin deposition. 

α-TP was prepared in different candidate formulations; 2% α-TP solution in a 20:20:60% (v/v/v) propylene glycol: ethanol: Tris buffer (0.1 M) vehicle at pH 7.4 (F1), 2% α-TP lotion at pH 6.8 (F2), and 2% α-TP carbopol gel at pH 6.4 (F3). A topical dose of 9 mg/cm2 from the three formulations was applied for 3 h to test the α-TP skin deposition in the stratum corneum (SC) and remained skin (RS) using the stripping method. Furthermore, skin deposition of α-TP from F1 was observed after 3, 6, and 24 hours. For sunscreen formulation, the SLNs are prepared by precipitation method5. The SLNs are evaluated for α-TP encapsulation, particle size, polydispersity index (PDI), zeta potential, and α-TP skin deposition.

The skin deposition studies demonstrated that when α-TP administered in a pH 7.4 vehicle (F1, HD size 10 nm) showed a higher deposition in the SC at 3 hours although it was not statistically significant (31.58 ± 13.19 µg/cm2 vs. 25.36 ± 3.93 µg/cm2 vs. 24.13 ± 10.50 µg/cm2, p > 0.05) and a similar deposition in the RS (4.76 ± 2.45 µg/cm2 vs. 4.49 ± 2.32 µg/cm2 vs. 3.70 ± 3.40 µg/cm2, p > 0.05) compared to the lotion (F2) and gel (F3) formulations, respectively. The skin deposition of α-TP from F1 in SC increase when increasing the application time from 3 h to 24 h (31.58 ± 13.19 µg/cm2 vs. 63.65 ± 13.32 µg/cm2, p = 0.046, one-way ANOVA with Dunnett’s multiple comparison tests). This effect was not as pronounced with regards to penetration into RS (4.76 ± 2.45 µg/cm2 vs. 11.83 ± 9.21 µg/cm2 p > 0.05). Finally, α-TP loaded SLNs exhibited a size in the nanoparticulate range (41.81 ± 0.74 nm), PDI of 0.20 ± 0.01, zeta potential of -2.89 ± 1.00 and demonstrated an interesting EE (87.50 ± 17.50%).

The enhanced α-TP penetration into the SC from the vehicle at pH 7.4 when applied for 24 h was due to the formation of nanoaggregates which readily deposited into the SC. The α-TP loaded SLNs were characterized by valid size and good EE. This result confirms the suitability of the sunscreen formulation employed in the present work for further in vitro testing investigation into the role of SLNs in enhancing α-TP penetration through human skin.

1. Young, A. R. et al. Sub-optimal Application of a High SPF Sunscreen Prevents Epider-mal DNA Damage in Vivo. Acta Derm Venereol 98, 880–887 (2018).

2. Wu, Y. et al. Antioxidants add protection to a broad-spectrum sunscreen. Clin. Exp. Dermatol. 36, 178–187 (2011).

3. Matsui, M. S. et al. Non-Sunscreen Photoprotection: Antioxidants Add Value to a Sunscreen. J. Investig. Dermatology Symp. Proc. 14, 56–59 (2009).

4. Saleh, M., Lawrence, K. P. & Young, A. The Photoprotective Properties of α-Tocopherol Phosphate Against Long-Wave UVA1 (385 nm) Radiation in Keratinocytes in Vitro. (2021) doi:10.21203/rs.3.rs-275304/v1.

5. Heurtault, B., Saulnier, P., Pech, B., Proust, J. & Benoit, J. A Novel Phase Inversion-Based Process for the Preparation of Lipid Nanocarriers. Pharm. Res. 19, 875–880 (2002).

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